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Share your CSS knowledge

nickytonline profile image Nick Taylor (he/him) Updated on ・1 min read

Today I learnt about the :placeholder-shown pseudo-selector thanks to Daniel’s Tweet.

What are some things about CSS that you've learnt about recently or something you already knew and think others would benefit from knowing?

Let's talk about it


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Several tricks that I used very often:

Select all the elements with same class except for the first one

While you complaining there's no :not(:first-of-class) selector, you can do this instead:

.foo + .foo {
  margin-top: 1rem;

Mimicking grid-gap without using grid layout:

.album {
  --gap: 1rem;
  padding-top: var(--gap);
  padding-left: var(--gap);

.album > .photo {
  margin-right: var(--gap);
  margin-bottom: var(--gap);

Clear all the predefined styles

a {
  display: block;
  text-decoration: none;
  /* blah blah blah... */

a.logo {
  /* This disables all the rules defined above */
  all: unset;
  /* start from fresh */

I never knew about all! Thank you for this!


object-fit is one I haven't used too much until recently (due to browser support). Once you can finally get off that IE11 train the web world really opens up!



My favorite thing about object-fit is that you can use it with img srcset for responsive background images! The picture element is cool if you really need to be serving differently cropped images, but whenever I can get away with same aspect ratio and not supporting IE, I always use object-fit + srcset for all background images.


Definitely a good use case! Did this myself in a recent project in fact.


isn't is similar to background cover?


Indeed it is, but can be used on replaced elements, such as image and video


This property comes in handy when using the img selector, it could be responsive very good one tho!.


I didn't learn this recently but I tend to forget it from time to time.

The nth-child() selector every now and then throws me off.

I don't know why but I always interpret it like "select the nth child of this element", when in reality is "select this element if it is also the nth child of its parent", to put it in code, let's say we have this structure:

<div class="parent">
    <div class="child"></div>
    <div class="child"></div>
    <div class="child"></div>

If I want to select the first div with the class name "child", I always first write .parent:nth-child(1), then realize my mistake when the code is not working and rewrite it as .child:nth-child(1)


Wow...today I learned. Thank you ;)


That made me think of this funny Tweet from @chriscoyier today about position sticky.

I think CSS variables are starting to gain steam. It makes a lot of sense for theming. DEV, for those who aren't aware, uses CSS variables quite a bit for theming.

@davidkpiano recently talked about his heavy use of them for animations on a recent episode of Shop Talk.

Him and David Shaw have this awesome Twitch stream where they reverse engineer animations. They're called the Keyframers and you can follow them on Twitch or on the Twitters.

It's really an amazing thing to watch.


As I learned instead of writing six lines of JS to lock a nav bar I place, position:sticky; took care of it.


I tend to have multiple languages on my presentations and use the :lang() pseudo-class to tweak the styles for phrases/sentences that are not the main language.



What, I never heard of it! Awesome!


Using the tilda to target siblings has huge use cases

.oneElement ~.anotherElement


Yes! It even allows things such as "select all the li if there are more than 6 li(s)"

Very useful indeed.


Transition does not work for display : none


I once used :placeholder-shown thing to make a material design like floating input label.


I LOVE absolutely positioned ::before and ::after pseudo-elements. I usually use them to either draw lines underneath elements or additional boxes the full size of the element, which you can do wackier things to (like transforms) than using things like borders or background colors.

Example of an underline for a link:

.link {
    position: relative;

.link::after {
    /* 'content' value is required - this is just blank */
    content: ""; 
    position: absolute;
    display: block; 

    /* matches the width of the nearest position: relative parent */
    width: 100% 
    height: 2px;

    /* anchor it to the bottom-left corner */
    bottom: 0;
    left: 0;

    background-color: purple;

I use them all the time, so I set up a little SASS mixin to save some keystrokes and clean up my code:

/* the mixin (simplified version) */
@mixin pseudo($type) {

    content: "";
    position: absolute;
    display: block;

    if($type == width) {
        width: 100%;

/* the code above with mixin */
.link {
    position: relative;

    &::after {
        @include pseudo(width);
        height: 2px;
        bottom: 0;
        left: 0;
        background-color: purple;

Once you start playing around with them you'll find there's all kinds of fun stuff you can do without having to change the HTML at all!


I'm very much taken by display:contents at the moment. When creating different cases in responsive layouts, the ability it gives to flatten the box tree has a surprising number of uses.


:not can be stacked, to allow for multiple classes to be excluded:

.grid:not(.blue):not(.red) { }

This is because .grid:not(.blue), .grid:not(.red) will include both supposedly excluded classes as one includes the other.


Recently, in an effort to refactor (read rewrite) an app that was terribly written (like really really badly to the point of creating BIG security holes) I learned a lot of new things about css and scss (and React, and webpack, and Jest, and TDD, and security driven development, and...). From CSS Grid to beautifully manage the general layout of the page to css variables for theming (thanks for that Dev.to), with @mixin and @import ... soo many things to create clean, short, organized and efficient css styles


place-items - shorthand for align-items and justify-items
place-content - shorthand for align-content and justify-content


One I learned and others seem to have missed also is justify-content: space-evenly. Instead of space-around or space-between. When using flex-box.


Not supported in IE and not complete support in Edge by the way 😬


Made use of the :first-of-type pseudo-class fir the first time.


Place-items can be used in place of
justify-content and align-items